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In a turbulent tradition

30 April, 1998 | By BY BARRIE EVANS

technical

The cliche is that we are in the age change, an exceptional period in history. The still-ascendant nostalgia industry supports this view by imaging the past as a contrasting retreat into continuity. Some in earlier times might well disagree, though, such as those whose ways of life were turned upside down by the industrial revolution, or those who have felt forced to emigrate. Firms like Bulmer Brick & Tile Co have survived these cycles of historical change because in each period they have found contemporary business opportunities for their largely-traditional technology.

Bulmer's first documented records are of tile making, from 1450. But post-war the kiln was being used to fire pottery. And while local brickmakers all once made some stock bricks, today Bulmer makes none, nor tiles. The 1990s Bulmer business is a just-in-time niche supplier of custom brick and terracotta. Much is for restoration work but by no means all. In 10 years time who can be sure what the product focus will be?

All through the process of making and delivering products we see today's demands refocusing the technological process.

From earth to fire

Once Bulmer was a local brickworks for the Sudbury area in Suffolk. Today it supplies matching bricks to anywhere from the Isle of Wight to the north of Scotland. Surprisingly, probably 99 per cent of matching is done by the blending and firing of clays from its Sudbury works site. Clay is brought in only to match Suffolk whites.

Clay used to be dug in winter and fired in summer; drying conditions are better then and building work was more seasonal than it is today. Since the men were on piece-work they picked out the best clays. So over recent years Peter Minter, who runs Bulmer, has had to organise a (gentle, mechanical) extraction sequence of digging the clay to restore the quality balance.

Earth is piled in the open, fairly friable, and not piled too high so that the material at the bottom does not get crushed. It is converted to a mouldable clay fairly readily in a pug mill and tempering pit and is near stone-free. Clay needs very little extra preparation for finer application as terracotta. (Terracotta, for Minter, is fired earth, thus any piece that is not a brick or tile. Usually it is decorative, moulded and/or cut.)

Brick and terracotta are generally hand-thrown into wooden moulds. Wooden blocks can be added to moulds to vary shapes, say to create squints. For some regular items, such as some bricks for cutting, the moulds may be aluminium alloy, which has an open-textured surface that takes the sand which ensures demoulding.

The mould shed holds a stock of some 500 moulds, about a quarter of which are in periodic use. Some go back to the last century.

Bricks are typically dried outside in hacks - low-roofed, open-sided shelters. Other pieces are dried at one end of the moulding shed, sometimes with heat and dehumidification. The biggest pieces can be a solid lump of 40kg of clay or more, taking six to eight weeks to dry depending on the time of year. Spring is the worst time for drying.

Allowance is made for losses of 10 per cent, most of which arise in drying rather than firing. For an order of just a few big pieces, double the quantity may be made. One of the skills of mould-making is shaping the clay to allow for subsequent shrinkage in drying and firing, which may reach 12.5 per cent. Some items, such as elaborate finials, may be composite, made of several pieces threaded over a stainless steel rod, bedded in lime mortar (or on occasion epoxy is used).

Kilns have been coal-fired here since the 1600s. The current kiln dates from 1936. The domed roof was rebuilt two years ago during the winter, the maintenance season. A wall of straw bales and some heating kept frost effects at bay. If it is used solely for brick the kiln's capacity is 10-12,000 bricks. In the season it takes about seven days to load, fire, cool and unload. There were 22 firings last year.

The kiln is run by feel rather than instrumentation, a matter of experience. (Minter is attuned enough to the sights and sounds to know who is stoking the coal from the ring of his shovel.) Even so, small variations in temperature, weather and position of items in the kiln contribute to the characteristic variation in finished products. The first firing of the year, when the kiln is relatively damp, needs particular care with control.

Some matching to dark colour/glaze can be achieved. River muds were often used for glazed headers - the glaze a product of minerals and salt. A sheen can be given by firing to a higher temperature. A green tint for bricks at Herstmonceaux was created with a mixture of copper and cobalt. Salt glazing is risky because this relatively brittle skin may delaminate.

Cutting and rubbing

Rubbed brick arches are common enough, but the skills needed for repair and replacement are increasingly rare. One service Bulmer provides is brick arches, delivered to site in a box, including centering and spacers between bricks to show the specified joint widths. Despite this prefabrication, there are occasional complaints from site about pieces left over, which turn out to be because joints have been made too thick or arches otherwise wrongly built.

Some five years ago English Heritage encouraged Bulmer to build up its brick-cutting side to support the refurbishment of Hampton Court. Brick- cutting is basically simple. Ply templates of the shaped corbel or other bricks needed are made and clamped either side of a whole brick. The brick projecting beyond the template is cut away with saws and files - see illustration. By turning the brick through 90degrees and clamping on the templates again, it can be cut to create a corner brick. Time was when bricks were rough- cut in the factory and finished on site to line through exactly. Such site skills are no longer assumed to be available.

Bulmer bricks are relatively soft, though durable. Bricks can be either cut or specially moulded to shape. Minter does not see any difference in quality or appearance between a cut and dressed (abrasive-rubbed) brick and one that is moulded and dressed. The choice is based on quantity and urgency, and thus cost.

Improving the specifier

Minter is a brick fan, though he finds little to admire in the twentieth century. Lecturing and taking groups of students round the works are investments he makes in a hoped-for future of better-quality brickwork.

And what does he think of architects and surveyors as specifiers? The drawings look good, with a cad precision. But they may not be precise enough if brick dimensions are not well understood, especially imperial ones. For example, he says, it is no good translating a nine-inch brick as 225mm. Also, drawings may look finished but do not always demonstrate a practical understanding of how brickwork will be built.

He finds architects wanting too much uniformity in matching, at least until they see the finished product. Sometimes they have only a limited feel for the production process, such as the need for drying time and seasonality. So too for materials, sometimes believing the hardest brick is the best.

While Minter has come to terms commercially with the lack of site skills, he suggests architects should make use of what site skills there are whenever possible, otherwise the skills that are left will die.

Another few centuries

As to the future, Minter expects some diversification of products. Some floor bricks and copings are made, there could be batches of mathematical tiles or decorative ridge tiles. He may move further into the decorative market with small batches of finials or decorative tiles.

Some orders come through specialist brick merchants, say for a few hundred bricks. Bulmer sells some lime and brick dust. This dust is pozzolanic (partially substituting for cement in some repair applications); it could be better used if an organisation such as English Heritage developed a standard for it, Minter feels.

He plans a second kiln, but the recent kiln refurbishments have improved existing capacity and so delayed the need for this investment. What is built depends partially on the product mix that is developing. And, perhaps the key element in future continuity, Minter's son is there to take over from him.

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